JPS6077505A - Noise suppression circuit - Google Patents

Abstract

PURPOSE:To improve the suppression effect of noise by adding a diode to a differential amplifier and adjusting the current applied to the diode with an independent control system so as to control the noise suppression independently of a signal system. CONSTITUTION:A bias power supply 14 is connected to a base of the 1st transistor (TR)1 of a noise suppression circuit and an emitter resistor 3 is connected to the emitter. Moreover, an emitter 4 is connected to the emitter of the 2nd TR of the same conduction type as that of the TR1 and an output terminal 10 is connected to the base. A common connecting point S of the resistors 3, 4 is grounded via a constant current source 12 and the collector of the TRs 1, 2 is connected to a power supply voltage 11 via load resistive elements 5, 6. Furthermore, the cathode of the 1st and 2nd diodes 7, 8 is connected to each collector of the TRs 1, 2 and the anode connected in common is grounded via a constant current source 13. Then noise is suppressed independently of the signal system so as to improve the noise suppression effect.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a noise suppression circuit, and particularly to a noise suppression circuit having a control system independent of a signal system.

[Prior art]

Conventionally, there have been some types of noise suppression circuits.

In Figure 1, diode DIID2 and resistor R(
It also has an input terminal (a) and an output terminal (s).

Now, assuming that the input terminal aK input voltage vl is given, the following relationship is obtained, ■V,=Vingo;-+RI,...
...(tl where W, V,: thermal voltage, 1B = reverse saturation current.

17 = current flowing through the circuit, output terminal bK is output voltage v0, V, = R1, ......
An output voltage of (2) appears.

Letting the impedance of the diode DI O and rl be rl and r, respectively, r+=rz=upper:L,=-9−−−−−−−−0,
-0, (3+qI) where k: Hornmann's constant, T: absolute temperature.

q: The impedance of the charge diodes D+ and Ds is the (
3) As shown in equation 5, the currents I and K flowing through the circuit are inversely proportional, and from equation (1), the input voltages V and K are also the output voltage V. The characteristics of the gain G=RI blade/V+ with respect to the input voltage V, T/ of the input voltage V, are shown in FIG. 2 using the resistance value R as a parameter.

In this figure, R1, R1, Rs are arbitrary iv of resistor R
express. As shown in Figure 2, the output gain is large for an input with a high signal level, but the gain is small for an input signal with a low level, so the feature of this circuit is that it suppresses noise that is weak compared to the signal. Used as a noise suppression circuit.

For example, when used for the purpose of removing noise contained in a video signal, the video signal is filtered through P, F, (low-pass filter) and H, P, F, (high-pass filter) to remove high-frequency noise. Separate and extract signals containing components. After that, the above signal is passed through a noise suppression circuit, and the signal-to-noise ratio S
/NvGood() method is used.

However, in such a noise suppression circuit, the amount of noise suppression can be arbitrarily set using the resistor R, but on the other hand, it is determined as the load impedance of the signal equal to the resistor R.
Therefore, it is difficult to say that the amount of noise suppression can be set arbitrarily. Since the control system for TRS and noise suppression overlaps with the signal system, there is a drawback in that it particularly adversely affects the frequency of the signal.

[Summary of the invention]

This invention was made to eliminate the above-mentioned drawbacks, and provides a circuit that can control noise without adversely affecting the signal by providing a control system independent of the 4N system. '51C. This invention will be explained below.

[Embodiments of the invention]

FIG. 3 is a circuit diagram showing an embodiment of the present invention.

In this figure, 1 is a first transistor, 2 is a second transistor, and emitter resistors 3 and 4 (with resistance values Y R, and RI, respectively) are connected to the emitters of both transistors 1 and 2, respectively. ) is connected, and the common connection point S of emitter resistors 3 and 4 is a constant current source 121
It is grounded through. Collector of first transistor 1.

A power supply voltage 11 is supplied to the collectors of the second transistors 2 through load resistance elements 5 and 6 (respectively t'L resistance values t' RLI and RL). No.! The cathode of the first diode 1 is connected to the collector of the transistor 1 of R2, the cathode of the diode 8 of R2 is connected to the collector of the second transistor 2, and the common connection point of both diodes 1 and 807 node is It is grounded via a current source 13. Also, 9 and 1o are input terminals.

14 indicates a bias fl source.

Next, the operation will be explained.

In Fig. 3, input terminal 5Vcvl, input terminal 10
When an input KVH is applied, the diodes 1.8. In the case where the constant source 13 is added, the well-known input/output characteristics of a differential amplifier are shown. diode? , 8, and this generator 8 equipped with a constant current source 13
At A, when the input v112<v□, the load current I0 flowing through the load resistance element 6 decreases, and the voltage drop due to the resistance values RL and K becomes small, so the potential at point q increases. On the other hand, as the potential at point q rises, the current flowing through the diode 8Vclin increases, and this current causes a voltage drop due to the load resistance element 6, working in the direction of suppressing the rise in potential at point q.

That is, it means that the bare Vc of diodes 1 and 8 provides a negative feedback effect to the differential amplifier.

If we treat the input/output relationship quantitatively, we get the following 5.

According to Fig. 3, α■ is calculated from Kirchhoff's law for the voltage at the common connection point S.

Vmr　Vy　In□−αIaRg 1 (l-α)I.

”Vat Vy In (1-α)1.R,・-・・
・-=-(41s Similarly for diodes 7 and 8, +, &: Koyama-kai 1z W- Tsude-ma V Sot
Then, regarding the output voltage, Ver = Vcc (α■.+βI l) RL −−
--(71Vox=Vcc l (1-α published l-β)
L) RL-...(sl relationship holds true).

Here, α and β are current distribution ratios for Ia and I+Vc, respectively, and 0<α<1. O(βkl. Also,
■. , ■ represent the current value of the constant current source 12.13.

From the above formula, the great sword (V,, -VIl, ) K vs. -11
tj (Vo, −V・mean) can be calculated theoretically. Using the current value I as a parameter, the gain with respect to the input voltage is calculated using a numerical counter n, and the result is shown in FIG. 4.

From FIG. 4 to Figure 5, the gain-manpower characteristic curve is controlled by the current value In. For example, when removing noise added to a video signal, H, P, F.

By suppressing the noise after passing through the signal, only the noise can be suppressed without drastically attenuating the signal, and furthermore, the amount of this suppression can also be controlled by the DC voltage. This situation is shown in FIG.

In Fig. 5, (eye) is a video signal that contains noise N, and becomes as shown in (C) when H, P, and F are passed through the buttons. Q is the amount of suppression, and by suppressing the noise N part, only the signal can be obtained as in (IT).

FIG. 6 shows another embodiment of the invention.

This is a circuit in which resistors 15 and 16 are inserted at 7 nodes of diodes 1 and 8. In this way, insert a resistor of 15° and 16°.
This has the effect of changing the negative feedback control characteristics of the differential amplifier using the pair of diodes 7 and 8.

〔Effect of the invention〕

As explained above, this invention adds a diode to the differential amplifier and provides an independent control system to adjust the overcurrent of this diode K This has the effect of controlling the amount of suppression.

[Brief explanation of the drawing]

FIG. 1 is a conventional noise suppression circuit, FIG. 2 is a curve diagram of gain-human power characteristics in the circuit of FIG. 1, FIG. 3 is a diagram showing an embodiment of the noise suppression circuit of the present invention, and FIG. The gain-manpower characteristic curve diagram in the embodiment shown in Fig. 3, and Fig. 5 show H, P, F,
FIG. 6 is a schematic diagram showing how noise in a video signal is suppressed after passing through a high-pass filter (high-pass filter). In the figure, 1 is a first transistor, 2 is a second transistor, 3.4 is an emitter resistor, 5.6 is a load resistance element,
1 is the first diode, 8 is the second diode, 9 is the input terminal, 10 is the output terminal, 11 is the power supply voltage, 12.13
is a constant current source, and 14 is a bias 1 source. Note that the same reference numerals in the figures indicate the same or corresponding parts. Agent Masuo Oiwa (2 others) Figure 1 1 Figure 2 - Human power Figure 3 Figure 4 Figure 5 (1) (It) (Ill) (lv) Figure 6 Procedure amendment (voluntary) Showa Tough 1, January 77, 2016, Case description: Japanese Patent Application No. 58-1880813 2, Name of the invention: Guo & Suppression Circuit 3, Person making the amendment Representative: Hitoshi Katayama Department 4: Agent 5, Drawing subject to amendment 6, Amendment The content drawings, Figures 2 and 6, have been amended as shown in the attached sheet. that's all

Claims (1)

[Claims] The emitter resistor of the emitter KIEI of the first transistor is connected to which the bias voltage is applied to the pace;
A second emitter resistor is connected to the emitter of a second transistor of the same conductivity type as the first transistor whose base is input, and the common liquid α point of the first and second emitter resistors is The first transistor is connected to a differential amplifier that is grounded via a constant current source and a power supply voltage is supplied to the collectors of the first and second transistors via first and second load resistance elements, respectively. 1st to the collector of
The cathode side of the second diode is connected to the collector of the second transistor, and the common connection point of the seven nodes of the first and second diodes is a constant current source! A miscellaneous "suppression circuit" characterized by being grounded through the